In the past, the integration of communications to the general purpose computer (e.g. the personal computer) functional environment has been either highly specialized, or expensive and limited in capability.
In simplest form, a computer can control communications by means of a modem, which interfaces directly with a telephone line. A telephone switching system receives digits and controls the progress of a call as if it were a telephone call. There is no possibility of providing enhanced services by controlling the switching system itself from the computer.
Computers have been connected to lines or trunks in a central switching (e.g. PABX) system, or to a main switching system bus, in order to automatically detect the number of an incoming call and to provide, to an operator on the computer screen the name and other details of an incoming caller immediately upon the operator answering the call. In this case the computer obtains the incoming call number and merely accesses a database stored in its memory, and provides data to the operator by displaying the database information on it display. There is no possibility of controlling the functioning of the switching system itself.
It would be desirable to be able to detect that the calling party has a videophone or enhanced set that can display live rate video, to access a video commercial or promotion associated with the PABX related to the types of products the calling party is known to favor, resulting from record of past purchases, to configure the PABX to establish a wideband channel to the calling party, and to play the commercial or promotion while the calling party is waiting for service by an operator. This is not possible to do at the present time. While a computer can be connected to a PABX to perform sophisticated functions via a host command interface (HCI) trunk, it cannot reconfigure the PABX itself to provide enhanced services.
As another example of a computer to communications device interface, a fax modem server is connected to a local area network (LAN) to which plural computers are connected, whereby plural computers can share the services of the fax modem via the LAN. In present systems only the specialized services of the fax modem can be provided, and obviously this is restricted to fax functions only.